1. Technical Field
This invention relates to optical receivers, especially but not exclusively optical receivers for use in optical interconnects.
2. Background Art
Optical interconnects are used to convert optical signals to electrical signals and vice versa. They are used in optical communications systems, for interconnections between equipment, such as computers, which transfer data at high rates, and within such equipment to transfer data between components such as integrated circuits.
The typical optical interconnect comprises an interconnect transmitter which converts electrical pulses representing digital data into pulses of light for transmission via an optical transmission path, which might be free space. An interconnect receiver at the other end of the transmission path converts the pulses of light back into electronic pulses for processing by electronic circuitry.
Optical interconnects for inter- or intra-computer communications may comprise a multiplicity of links requiring perhaps thousands of receivers in an array on a miniature device such as an integrated circuit. Consequently, such receivers must be small and have a low electrical power consumption, yet still be highly sensitive and fast.
A typical receiver comprises a photodetector to receive the light pulses and convert them into electrical pulses which will then be amplified and processed in known manner. The light-absorbing area of the photodetector is critical to the performance of the receiver. The input capacitance of the receiver is dominated by the capacitance of the photodetector, so it is usual for known optical receivers to have a detector with a small area, and hence small input capacitance, which will reduce the time constant and lead to improved bandwidth and sensitivity. Unfortunately, reducing the area of the photodetector makes it more difficult to align the input light beam onto the absorbing region of the photodetector. This can result in problems, especially where a large number of receivers must be provided in a small area, such as when interconnecting integrated circuits and other components.